|

||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

PT0289(07/07)

Ver: 0

5

The PT7M7443~7452 /RESET output is pulse asserted

once for the reset timeout period after each valid manual

reset input condition. At least one manual reset input must

be released (go high) and then be driven low for the

extended setup period before /RESET asserts again.

Internal timing circuitry debounces low-to-high manual

reset logic transitions, so no external circuitry is required.

Figure 9 illustrates the single manual reset function of the

PT7M443/7444 single-voltage monitors, and Figure 10

represents the dual manual reset function of the

PT7M7445/7446 and PT7M7449/7450.

The PT7M7447/7448 and PT7M7451/7452 include both

an extended setup period and immediate setup period

manual reset inputs. A low-to-high MR2 rising edge

transition immediately pulse asserts the /RESET output for

the

reset

timeout

period

(140ms

min).

If

the

PT7M7447/7448 and PT7M7451/7452 MR2 input senses

another rising edge before the end of the 140ms timeout

period (Figure 11), the internal timer clears and begins

counting again. If no rising edges are detected within the

210ms timeout period, /RESET deasserts. The high-to-low

transition on MR2 input is internally debounced for 210ms

to ensure that there are no false /RESET assertions when

MR2 is driven from high to low (Figure 12). The MR2

input can be used for system test purposes or smart-card-

detect applications (see Applications Information section).

The PT7M7449~7452 monitor the voltage on RSTIN using an

adjustable reset threshold set with an external resistor voltage-divider

(see Figure 14). Use the following formula to calculate the externally

2

1

+

×

=

the reset input threshold (0.63V). Resistors R1 and R2 can have very

high values to minimize current consumption because of low leakage

currents. Set R2 to some conveniently high value (250k, for

example), and calculate R1 based on the desired reset threshold

voltage, using the following formula:

×

=

1

2

1